1. Technical field
The present invention relates to a liquid crystal composition and a liquid crystal device comprising a liquid crystal layer comprising the composition, and more particularly to a liquid crystal device advantageously usable in a liquid crystal device employing a guest-host (hereinafter also referred to as GH) mode.
2. Related art
A display device is required to have a high level of visibility and a low consumption of electric power. As one of display devices having such qualities, GH-mode display devices, capable of displaying brightly, have been known, and is expected as a high-quality display device employing a reflective mode.
A liquid crystal composition comprising a dichroic dye having a particular group and a host liquid crystal, and a liquid crystal device employing a GH-mode are disclosed in Japanese Laid-Open Patent Publication “Tokkai” No. 2004-75821.
The switching of the liquid crystal device is usually carried out by varying the alignment state while applying (ON) and not applying (OFF) an electric field to liquid crystal. The alignment variation of liquid crystal without an electric field is affected by a force of alignment layer, and, thus, the response speed may become to lower while not applying an electric field to liquid crystal.
A dual-frequency switching method has been known (see Applied Physics Letters, Vol. 25, No. 4, 186-188(1974); and Applied Physics Letters, Vol. 41, No. 8, 697-699(1982)). This method employs a dual-frequency switchable liquid crystal, of which dielectric constant anisotropy, Δε, changes from a positive value to a negative value with increasing the frequency of applied voltage, and therefore allows a reversible change of the liquid crystal alignment with an electrical field. According to this method, it is possible to carry out the switching in the manner that liquid crystal molecules change their alignment actively, and, thus, to improve the response speed. It is, however, impossible to store image information without an electrical field, and, thus, it is necessary to continue to apply voltage to liquid crystal for maintaining images.
As a dual-frequency switchable liquid crystal, there has been provided liquid crystal exhibiting a nematic phase (see Mol. Cryst. Liq. Cryst., 49, 83-87 (1978)).
It has been required to provide a liquid crystal device exhibiting a high displaying contrast and capable of storing image information.